Bahrain riot police watch as a protester holds up a picture of jailed political leader Hassan Mushaima with the words "Mushaima is in danger," during a protest in Duraz, Bahrain, on Friday. Mushaima's son is on the list of people whose citizenship has been revoked.

By Ian Johnston, NBC News

Bahrain’s government said Wednesday that it had revoked the citizenship of 31 Bahrainis, described by human rights activists as mostly former political detainees.

They called on the United States, U.K., United Nations and others to put pressure on the Bahraini authorities to reverse the decision and allow freedom of expression, and also to “immediately stop the systematic and widespread human-rights violations.”

'Damage to state security'Bahrain, a small island kingdom, is an important ally of the United States as it is home to the U.S. Navy's Fifth Fleet. There has been significant unrest since pro-democracy protests erupted last year as the Arab Spring movement swept the region.

The Bahrain News Agency published a brief statement by the Ministry of Interior that cited a law allowing “the re-evaluation of nationality when a holder of the Bahraini citizenship causes damage to state security.”

It then listed names of 31 people whose citizenship had been revoked, including Ali Hassan Mushaima, the son of the leader of the Haq movement, Hassan Mushaima, who is serving a life sentence.

“The Minister of Interior will take the necessary measures to implement this in conformity with the kingdom's commitments under international law,” the statement added, saying the people named would be able to appeal.

The human rights groups’ statement said the authorities had not provided “substantial evidence” explaining the decisions.

“It is apparent that the actions taken by the Bahraini authorities to revoke the citizenships of 31 individuals is intended to punish them for expressing peaceful dissent and thereby intimidate others from exercising their right to freedom of expression,” it said. “This comes at a time when the crackdown in Bahrain by the authorities is intensifying, and in light of continued international inaction, will continue to deteriorate.”

Mohammed al-Maskati, president of the Bahrain Youth Society for Human Rights, told NBC News that about 70 percent of the people on the list were former political detainees.

Some on the list are living abroad with at least eight in the U.K., and others in Iran, Iraq, Sweden and Australia. Some of those have been granted political asylum by other countries, al-Maskati said.

Security forces fire tear gas as they crackdown on pro-democracy demonstrators who have vowed to disrupt the race. Bahrain's monarchy is desperate to show the world that the country is a safe place for the race.

He said it remained to be seen what the legal status of the men would be.

“We don’t know what action they will take against them, if they will ask them to leave the country or they will let them … take their case to the courts. We don’t know what legal status they will find themselves in now.”

Ina separate statement, the Bahrain Center for Human Rights said it was concern at reports that a detainee, Adnan Al-Mansi, 22, had been subjected to “severe physical torture, including sexual assaults” after his arrest.

The center said al-Mansi had been accused of making a bomb, but it said he was “a prisoner of conscience detained solely on the basis of his political opinion.”

NBC News requested a comment from the Bahrain Embassy in the U.K., but a response was not immediately received.